(1) Field of the Invention
The invention relates to an electroless gold plating solution, particularly a solution capable of plating exactly onto predetermined parts on the workpiece.
(2) Description of the Prior Art
Electroless gold plating solution containing a thallium or lead compound are known, as disclosed, for example, in JP 56/152958, which increases the deposition rate of gold, and helps crystal growth in the deposit and thus enhances the heat resistance of the latter.
However, such a compound tends to decompose the solution and cause gold precipitate at high concentrations. Therefore, the concentration should be limited to several ppm at the highest, which renders the solution very difficult in handling.
The present invention aims at elimination of this problem associated with such plating solutions, and provides an electroless gold plating solution which does not deliver gold precipitation even at high concentration of said thallium or lead compound, while retaining its advantages such as increased deposition rate and large crystallites of deposits.